Telephone interconnecting circuit



1931- R. FELDTKELLER ET AL 1,832,452

TELEPHONE INTERCONNECTING C IRCUI T Filed July 3, 1929 TFANSM/TTH? .67 (E 42 4.2 4 5 J 4 E. FELDT/ffLLE/i' A r TORNE f Patented Nov. 17, 1931 UNITED STATES, PATENT OFFICE RICHARD FELIDTKELLER, OF BERLIN, AND WALTER WOIQMAN, OF SIEMENSSTADT, MANY, ASSIGNORS TO SIEMENS '8: HALSKE AKTIENGESELLSCKAFT, OF SIEMENS- STAD'I, NEAR BERLIN,.GEBMANY, A COMPANY OF GERMANY TELEPHONE m'rnnoonnnormo omoux'r Application filed July 3, 1929, Serial No. 375,628, and in Germany August 15, 1928.

The present invention relates to intercou- 30 used in other types of signaling systems, and

in cases where only one of the interconnected circuits transmits and all of the rest receive waves from this one circuit. An instance of the latter use would be the supply 15 to several receiver circuits-0t news, entertaininentor the like. a

An object of the invention is to associate three or more circuits together bymans of an impedance network proportioned so that 20 the total impedance presented to each circuit is substantially equal to the impedance which the circuit presents to the network. 7

A related object of the invention is to associate three or more circuits by an impedance network such that the attenuation between certain ofthe interconnected circuits is less than that between either of these circuits and another. v 1

Other features and objects of the invention will be apparent from the following detailed description in connection with the drawings in which:

Fig. 1 shows an interconnecting network of the general delta type.

Figs. 2 and 3 show star connected networks.

Fig. 4 discloses a combination bridged-T network, and

Fig. 5 shows a distribution circuit for news, entertainment, etc., employing delta type networks for connecting the receiving circuits to the distribution circuit. 7

Referring first to Fig; 1, lines L L L and L are shown interconnected through the medium of the impedance network 11, 12, 13 and 14 and transformers 1, 2, 3 and 4. As indicatedin the drawings any number of lines may be connected together by an extension of this same plan, the resistance 11 and 14 star and being indicated (by the dotted line) as eventually connected together by still other similar resistances. The lines L L 'etc., may be ordinary telephone lines over which two-way conversatioiis pass or they may be other types of signaling lines, for either oneway or two-way transmission. The net work 11, 12, 13, etc., forms a closed circuit and is, therefore, an extension of the typ: generally referredto as a delta 'netwo'r Considering the line L its associated impedance 11 is in parallel with the series path including the impedances 12, 13, and 14 and the transformers 2, 3, and 4 and lines in shunt to these impedances. Impedance 11 is proportioned so that the total impedance represented by 11 and the rest of the system in parallel with it, is equal tothe impedance of the line L Repeating coil or transforim er 1 is preferably inserted to aid in making the impedance oi the line L at the point where it is connected to the network substantially equal to the impedance which the network presents to the line at this point.

This same relationship holds for each of the other lines so that each line is terminated by an impedance which is practically the same as the characteristic impedance of the respective line.

Since the incoming energy from any one line dividesbetweenallother outgoing lines it is fre uently necessary to employ amplifying repeaters to maintain the desired level on the difierent lines. One such am lifie'r 10 is shown connected in the line L 7 here a standard telephone repeater amplifier would give too great a gain, the use of a special amplifier may be avoided by including a resistance pad in series in the line.

The impedances 11, 12, etc., may be simple resistances or'may each be itself a network to simulate. a'ccuratel the impedance of the associated line in t e same manner that balancing networks in the prior art are made to simulate the impedance of a line.

The alternative or star type of connection is illustrated in Fig. 2 where lines L L and L are associated throu h individual transformers 20, 21 'and'22 with respective branches of a star network including series impedances 17, 18,a'nd 19. This scheme of connection can, of course, be extended to any desired number of lines. Amplifier 23 and resistance pad 16 are provided to serve the same purpose as repeater 10 and pad of Fig. 1. The amplifiers and if necessary the pads, may, of course, be supplied in the other circuits as well.

In this figure as in the case of Fig. 1, the impedances 17, 18, 19, etc., may be simple resistances or may he impedance networks and they are proportioned with respect to each ot er and to the impedanccs of the indi vidual llllGS to present to each line a total impedance substantially equal to the impedance of the respective line as seen from the network.

14 successively forked system may be built up by connecting networks of the type shown in tandem. Also it is not necessary to employ the same type of network at opposite ends of a. line. For example, the line L, of Fig. 1 may extend to and be connected with the line L of Fig. 2.

A simple star type network for interconnecting three lines, L L and L is shown in Fig. 3. The star connected impedances 30, 31 and 32 are connected as shown and the lines are preferably connected to the impedance network by individual repeating coils 27, 28, and 29 which aid in obtaining the matched impedance relationship between each line and the network as a whole.-

It will be observed that the star connected network of 3 can be replaced by a delta type network by merely connecting an appropriate impedance in shunt to a winding of each transformer 27, 23 and 29 on the network side of the transformer.

Fig. 4 shows an interconnecting network three lines in which a single amplifier sufiices. 1f standard telephone repeater were connected in each of the lines of Fig. 3 (L L and L this would, in many cases, give a disproportionately high gain, and impedance pads would need to be used as disclosed in connection with Figs. 1 and 2. For instance, the attenuation between any two lines of Fig. 3 is 0.7 napier while it is common practice for a mid-line telephone repeater to introduce an amplification corresponding to about 1.4 napier.

Referring to Fig. 4 lines L L187 and L are associated through respective transformers 33, 34 and 35 with an interconnecting network of the bridged-T type including equal impedances 36 and 37 shunted by an impedance 33, and the junction of the equal impedances is connected to a shunt impedance 39 across the network. By proper proportioning of impedances 38 and 39 the attcnuation between lines 17 and 19 may be made low compared to that between either line L and L and a third line L For instance, if impedance 39 is made very high while impedance 38 is made quite low the attenuation between lines L and L is low. On account of the low shunting impedance 38, on the other hand, the attenuation between line L and L is high as is also that between L and L Amplifier 40 in L which may be a standard telephone repeater makes up for the large loss in transmission between line L and either of the other lines. The use of transformer 34 enables the impedance of line L however, to be suitably matched to the total impedance of the system into which it works. This system, therefore, gives a practically reflectionless connection between lines L L and L A system proportioned as described above for Fig. 4 is not dependent upon the use of the particular type of network disclosed in this figure, but the proportioning of the impedances to fit the use of lines of different impedance may be carried out in other types of interconnecting networks.

It will be understood, of course, that transformers 33, 34 and 35 may be omitted particularly where the circuits to be connected are already of the proper impedance. This might be the case where a subscribers line, for example, is directly connected to the interconnecting network.

In Fig. 5 transmitter 40 supplies speech, news, entertainment, etc., over line 41 to a plurality of loud speakers 49, 50, 51 located at different points along the line. At each location a delta network is disclosed comprising for example, equal shunt resistances 42 and 43 with the third arm formed by the impedance of the loud speaker 49, which is associated, if desired, through a transformer 46 with the delta network. In similar manner loud speaker 50 is associated by transformer 47 with the network 44, 45. By proportioning resistances 42 to 45 the line 41 may be terminated practically free from reflection and the attenuation from transmitter 40 to each loud speaker is substantially the same. The loud speaker 51 by the aid of transformer 48 is adapted to the characteristic impedance of the line.

It will be understood that amplifiers disclosed in connection with several of the figures may be either one-way or two-way amplifiers in accordance with usual telephone practice.

What is claimed is:

1. An interconnecting circuit for more than two lines, comprising an impedance network including impedances and transformer windings to which said lines are connected, said impedances and transformer windings having impedance values so proportioned that the network presents to each line a total impedance substantially equal to the impedance which the line presents to the network.

2. In an interconnecting circuit for more than two lines, each two lines having a common junction point, an impedance network comprising impedances connected from each such junction point to another said impedances having impedance values so proportioned that the network presents to each line a total impedance substantially equal to that of the line.

3. A circuit according to claim 2 in which star-connected impedances have their outer terminals connected respectively to each such junction point.

4. An interconnecting circuit for three circuits comprising star-connected impedances having their outer terminals connected to junction points of the circuits, respectively, and a shunt impedance across two of the starconnected impedances, forming thereby a bridged-T network, said impedance having impedance values so proportioned that the total impedance of the network is matched to the impedances of the individual lines.

5. A circuit according to claim 4 in which the coupling between two of the lines is greater than that between either of the two and the third line, and an amplifying repeater in the third line.

6. A distribution system between more than two circuits, comprising a common distributing circuit including shunt network impedances across it adapted to transmit impulses originating in any one of the circuits to all of the other of said circuits, the circuits to be supplied therefrom being connected to the respective network branches, the network impedances being proportioned to match the impedances of the connected circuits respectively.

7. A system according to claim 6 in which transformers are connected in the individual circuits to aid in matching the impedances.

8. A circuit according to claim 1 in which the impedances have attenuation values so proportioned that the attenuation between one line and each of the others is high compared to that between said others, and'an amplifier connected in said one line to make transmission between it and the other lines substantially the same as between said other lines.

In witness whereof, I hereunto subscribe my name this 12th day of June, 1929.

Y RICHARD FELDTKELLER. In witness whereof, I hereunto subscribe my name this 12th day of June, 1929.

WALTER WOLMAN. 

